gas decreases not because the concept of defi has stopped or getting lose their hype, but the volume of trade in Uniswap is decreasing day by day, that's why ethereum gas is decreasing slowly, as you can see past day the volume trade on uniswap is about $300,000 per day, and today its was $130,000.
you can see the movement of trade volume here :
https://www.coingecko.com/en/exchanges/uniswap#statistics
the volume is increase depend on new project that listed on their exchange and trade on uniswap exchange, but from what i see now, their volume is getting decrease a bit and eth gas are decreasing to, as you can see on etherscan, uniswap contract is on top 2 on rank most used gas per day after tether contract, but when the volume on uniswap are decrease, automaticly the gas price is decrease to.
you can see the here which contract are the most used for transactions and give impacts to gas price :
https://etherscan.io/gastracker